The present invention relates to filtering separators, of the kind having a housing which is subdivided by a partition, provided with parallel rows of holes or slots, into a dust-laden gas space for receiving filter elements positioned in parallel rows and being impinged upon by dust-laden gas from the outside towards the inside, and a clean gas space. In addition, a chamber is provided in the housing for cleansing the filter element surfaces of a row by counterflow action and simultaneously covering of a part of the rows of holes of the partition. The chamber is arranged for supply of compressed air to at least one injector arranged to feed compressed air and secondary air to the row of filter elements to be cleansed, the chamber being receiprocatingly displaceable along the partition in periodic and intermittent manner. Hereinafter, such separators will be referred to as "of the kind described".
In known counterflow cleaning operations of filter elements of a filtering separator of the kind described, e.g. in accordance with the German Patent Specification No. 1,228,130, each filter element (which may be in the form of a tube or a bag) has allocated to it an injector operating with compressed air, (through which pulses of compressed air are supplied periodically), together with entrained secondary clean air from a clean gas space, in counterflow to the dust-laden gas. It is a disadvantage that the compressed air is initially utilized to impose impingement of the filter elements in counterflow to the dust-laden gas flow, (i.e. a power loss occurs), since a pressure which corresponds to the prevailing filter resistance and distinctly exceeds the same must be built up and be exceeded by means of the injectors. In view of the required compressed air operating briefly and applied in pulsed manner, the dust released from the filter surfaces, (in particular slowly dropping dust), has insufficient time to drop downwards into the dust collection space, so that after switching over to dedusting, the filter elements are immediately impinged upon again by a part of the dust freed. Furthermore, at first the filter surfaces acted upon by the pressurised gas bulge out but after the compressed gas flow they are knocked back violently against the inner spacing elements of the filter elements (carpet beating effect), so that dust particles still present in the filter material are freed and thereby enter the inside of the filter elements, and thus the clean gas.
In the counterflow cleansing of the filter elements hereinabove referred to in accordance with German Patent Specification No. 2,450,751, a chamber including one or more compressed air injectors is reciprocated in the clean gas space along a perforated or slotted partition of the housing, so that the filter elements supplied with compressed air via the partition holes are impinged upon and cleansed in counterflow with the dust-laden gas. To this end, the filter element rows beside the filter element row switched to cleansing by means of the compressed air injectors are covered by lateral flanges of plates of the injector chamber, so that the freed dust has enough time to drop and cannot settle again immediately on adjacent filter elements switched to dedusting. In this case, the supply of compressed air occurs via a control valve, whereas the required secondary air is fed to the suction side of the compressed air injector or injectors from the outside via a duct of larger diameter and a valve situtated therein and which is to be opened. Compared to the rapidly operating compressed air control valves, the inertia of such valves is so great that the maximum required secondary air is not secured, in any case, during compressed air pulses lasting no more than approximately 0.1 second. This arrangement is thus unusable in practice. In view of the utilisation of secondary air from the ambient atmosphere, this air must be brought to a temperature lying above the dew point in the case of dust-laden gases containing water. In cases where filters are used for cleansing inert gases (for example in coal dust plants), the supply of external secondary air is disadvantageous and not permissible under various circumstances.
In light of the above problems, it is an object of the invention to avoid or at least minimize the drawbacks of the aforementioned counterflow cleansing systems for the filter surfaces of filtering separators of the kind described, (often referred to as bag or tube filters), and to provide a simple and uncomplicated structure devoid of any control system for the supply of secondary air to the compressed air injectors.